1 files changed, 129 insertions, 0 deletions
diff --git a/src/pkg/go/types/conversions.go b/src/pkg/go/types/conversions.go
new file mode 100644
index 000000000..fcbaf7717
--- /dev/null
+++ b/src/pkg/go/types/conversions.go
@@ -0,0 +1,129 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements typechecking of conversions.
+
+package types
+
+import (
+	"go/ast"
+)
+
+// conversion typechecks the type conversion conv to type typ. iota is the current
+// value of iota or -1 if iota doesn't have a value in the current context. The result
+// of the conversion is returned via x. If the conversion has type errors, the returned
+// x is marked as invalid (x.mode == invalid).
+//
+func (check *checker) conversion(x *operand, conv *ast.CallExpr, typ Type, iota int) {
+	// all conversions have one argument
+	if len(conv.Args) != 1 {
+		check.invalidOp(conv.Pos(), "%s conversion requires exactly one argument", conv)
+		goto Error
+	}
+
+	// evaluate argument
+	check.expr(x, conv.Args[0], nil, iota)
+	if x.mode == invalid {
+		goto Error
+	}
+
+	if x.mode == constant && isConstType(typ) {
+		// constant conversion
+		// TODO(gri) implement this
+	} else {
+		// non-constant conversion
+		if !x.isConvertible(check.ctxt, typ) {
+			check.invalidOp(conv.Pos(), "cannot convert %s to %s", x, typ)
+			goto Error
+		}
+		x.mode = value
+	}
+
+	check.conversions[conv] = true // for cap/len checking
+	x.expr = conv
+	x.typ = typ
+	return
+
+Error:
+	x.mode = invalid
+}
+
+func (x *operand) isConvertible(ctxt *Context, T Type) bool {
+	// "x is assignable to T"
+	if x.isAssignable(ctxt, T) {
+		return true
+	}
+
+	// "x's type and T have identical underlying types"
+	V := x.typ
+	Vu := underlying(V)
+	Tu := underlying(T)
+	if IsIdentical(Vu, Tu) {
+		return true
+	}
+
+	// "x's type and T are unnamed pointer types and their pointer base types have identical underlying types"
+	if V, ok := V.(*Pointer); ok {
+		if T, ok := T.(*Pointer); ok {
+			if IsIdentical(underlying(V.Base), underlying(T.Base)) {
+				return true
+			}
+		}
+	}
+
+	// "x's type and T are both integer or floating point types"
+	if (isInteger(V) || isFloat(V)) && (isInteger(T) || isFloat(T)) {
+		return true
+	}
+
+	// "x's type and T are both complex types"
+	if isComplex(V) && isComplex(T) {
+		return true
+	}
+
+	// "x is an integer or a slice of bytes or runes and T is a string type"
+	if (isInteger(V) || isBytesOrRunes(Vu)) && isString(T) {
+		return true
+	}
+
+	// "x is a string and T is a slice of bytes or runes"
+	if isString(V) && isBytesOrRunes(Tu) {
+		return true
+	}
+
+	// package unsafe:
+	// "any pointer or value of underlying type uintptr can be converted into a unsafe.Pointer"
+	if (isPointer(Vu) || isUintptr(Vu)) && isUnsafePointer(T) {
+		return true
+	}
+	// "and vice versa"
+	if isUnsafePointer(V) && (isPointer(Tu) || isUintptr(Tu)) {
+		return true
+	}
+
+	return false
+}
+
+func isUintptr(typ Type) bool {
+	t, ok := typ.(*Basic)
+	return ok && t.Kind == Uintptr
+}
+
+func isUnsafePointer(typ Type) bool {
+	t, ok := typ.(*Basic)
+	return ok && t.Kind == UnsafePointer
+}
+
+func isPointer(typ Type) bool {
+	_, ok := typ.(*Pointer)
+	return ok
+}
+
+func isBytesOrRunes(typ Type) bool {
+	if s, ok := typ.(*Slice); ok {
+		t, ok := underlying(s.Elt).(*Basic)
+		return ok && (t.Kind == Byte || t.Kind == Rune)
+	}
+	return false
+}